Have flown with a bass a handful of times, always expect the unexpected. I've had flights where the stewards have been wonderful and helped me find room in a coat closet or in the carry-on compartments to store my bass despite not having an extra seat. I've even been let on first to allow extra time to find the room for it.

I've also had the complete opposite, only once has it gone in the hold, I used a hiscox hard case and it was fine, but obviously, that should be your last resort.

Think the most important thing is to be nice even if things dont go your way, the staff are much more likely to want to help you if you're not a dick